This invention relates to spark ignition engines and more particularly to a gasoline engine system using variable direct ethanol injection and engine shutdown for increased vehicle efficiency.
Hybrid automobiles are becoming increasingly popular because of their demonstrated fuel economy benefits. Hybrids usually combine a gasoline engine with an electric motor along with sophisticated controls to establish operating modes. Those who have analyzed electric hybrid vehicle operation have concluded that the fuel economy benefits come from three primary sources (excluding unusual aerodynamically shaped vehicles that are not fully functional). A first source of fuel economy benefit is the regenerative capture of energy derived from the vehicle's kinetic energy during vehicle braking. Regenerative systems usually include electric generators/motors, a high voltage battery and power electronic components. Thus, a portion of the vehicle's kinetic energy that would otherwise be lost to heat during braking is stored as electrical energy in the vehicle's battery.
Another source of hybrid vehicle fuel economy results from optimization of the traditional internal combustion spark-ignited engine to produce better specific fuel consumption numbers over its operating range. Typically, the optimization includes engine downsizing and the use of a modified engine cycle (such as the Atkinson cycle) that further lowers effective engine displacement, but improves thermal efficiency. An example of this approach is the Toyota Prius. More recent variants have employed larger engines (Honda Accord, V-6 hybrid) with cylinder disabling.
A third source of fuel economy benefits comes from the shutdown of the engine during deceleration and idle. During periods of engine shutdown, onboard electric power is used to keep critical auxiliary components in operation. Critical auxiliary components include power steering, power brakes and lights. A non-critical, though highly desirable, auxiliary is air conditioning. For extended periods of air-conditioner operation in hot climates, the engine must be restarted during idle periods when the vehicle is not moving to prevent excessive battery drawdown.
The breakdown of fuel savings from these three sources depends very much on driving cycle and environmental conditions (hot or cold), but for typical ambient temperatures and moderate cycles (modest acceleration and braking rates of 3 to 4 mph/sec), well over 75% of the fuel economy improvement comes from the optimization of the traditional internal combustion engine and shutdown of the engine during deceleration and idle. Regeneration, even under modest circumstances, is a relatively small contributor. This relatively smaller contribution results from the fact that, in general, only one axle is connected to the electric power train (and therefore available for braking energy recovery) and the braking energy of the other axle is therefore not even available for recovery. In such a configuration, front wheel drive is preferred since most braking is accomplished with the front brakes due to weight distribution and weight shift on deceleration. Further, because electric generators have to be controlled to avoid jerkiness in a regenerative system when the brakes are applied, a “feathering-in” strategy is used that wastes some of the kinetic energy associated with higher vehicle speeds. Also, the “round trip” efficiency of stored electrical energy is no more than approximately 60%.
U.S. patent application Ser. No. 10/991,774 filed Nov. 18, 2004 deals with optimization of the traditional spark-ignited gasoline engine to produce higher fuel efficiency by utilizing the separately controlled direct injection of ethanol to permit higher boost pressures without detrimental knock. Such a variable direct-ethanol injection gasoline engine can achieve improvements, close to those achieved in current versions of hybrids.
An object of the present invention is to further improve the efficiency and to get substantially the same or perhaps even better fuel economy benefits as a full hybrid in a direct ethanol injection engine.